1. Field of the Invention
The invention relates to the field of raster scanned color video display.
2. Prior Art
In raster scanned color video displays, color data is often stored for each pixel in a frame buffer. The color data can represent "red", "green" and "blue" (RGB) or can represent an address to a color lookup table.
In many displays a plurality of windows are simultaneously displayed with different sets of colors used in each window. It is often convenient in these displays to have a particular color code represent one color in one window, and for example, another color in the background or other windows. In other applications, it is sometimes desirable to have a particular code represent a color in some fields on the display and a shade of this color in other fields. There are other applications where it is desirable for a particular color code to represent more than a single color under certain conditions.
One method of having a color code represent more than a single color is to use additional bits of data for each pixel in the frame buffer which provide, in effect, bank switching or remapping within a color lookup table or a PROM. Assume that the color data in the frame buffer is represented by N-bits and N-bits are required to provide the RGB signals. If two additional bits are used to provide information which allows selection of different colors for a particular code then N+2 bits must be stored in the frame buffer for each pixel. A PROM for this application would have a capacity of 2.sup.N+2.N memory cells. In a typical application where N is equal to 24 bits, the amount of PROM capacity becomes very large and in practice prohibitive.
The present invention provides an apparatus which permits a single code to represent more than a single color without large memory capacity thus eliminating the undesirable interdependencies between programs running different windows. The present invention provides a softly configurable data selector to select different configurations for each pixel.